1. Field of the Invention
The present invention relates to a photometric method for cameras, particularly to a photometric method for cameras by which photometry in varied photometric sensitivity distributions can be achieved.
2. Description of the Prior Art
In cameras having an automatic exposure control of through-the-lens photometric type, the amount to be exposed to light is determined by a photoreceptor which measures the light for taking a photograph passed through a taking lenses. In measuring, however, there is a problem of photometric sensitivity distribution over an entire picture area, that is, the problem that, at which position of the entire picture area and to what degree of the amount of light, does the photoreceptor receive.
Generally, the configurations of photometric sensitivity distributions are classified as overall photometry, weighted photometry and spot photometry. Overall photometry is the photometric mode that all the luminance of an entire picture area is received by a photoreceptor without any weighting factor, for example, regardless of whether or not an object having high luminance is in the center of a picture area or in a corner thereof, the amount of exposure is the same.
Weighted photometry is the photometric mode in which a specific portion of a picture area (mostly, around the center of a picture area) is measured by giving weight to said portion, for example, when an object having high luminance is in a specific portion of a picture area, the photometry therein is higher in luminance than that measured when said object is in the other portion in the picture area.
Spot photometry is the photometric mode in wich the light from only a portion of a picture area is measured, and in this photometry, the measurement is generally performed by a weighted photometry or an overall photometry, wherein small weight is placed on the neighborhood, in some measure, of the center of a picture area.
However, in these photometry procedures, there are advantages and also disadvantages, therefore it is most desirable to manage a suitable photometric mode according to the states of objects and a photographer's intentions. Especially in a single lens reflex camera of through-the-lens photometric type, the configurations of photometric sensitivity distributions of cameras are determined depending upon the relative position of the optical system of the view-finder and a photoreceptor.
There are some types of cameras in which a plurality of photoreceptors are arranged to switch over from one photometric mode to the other, but in this case, not only a plurality of photoreceptors but also a complicated optical system are required. Therefore, despite it being useful to switch over from one photometric mode to another, the practical application has not generally been applied.